Glacier 15, Antisana, Ecuador: its glaciology and relations to water resources
Résumé
Besides the Lewis glacier in Kenya, Glacier 15 of Antisana, Ecuador (5760–4830 m, 0.28 km2) is the only one which provides regular information regarding glacier mass balance near to the Equator (Annual Report of the World Services for the Monitoring of Glaciers, WGMS 2005) to the scientific community. The surface of the glacier had been re-constructed using aerial-photogrammetry from 1956 to 1997. Since 1994, direct measurements have been taken over the terminal zone at the glacier tongue using topography. That process has shown the changes at the glacier limits and has determined the superficial speed at the terminal zone of the tongue (ablation zone). At the ablation zone (<5100 m) a wide net of stakes have been installed in order to measure the evolution of the glacier mass each month since 1995. In addition, holes to measure accumulation have been dug in the ablation zone at the end of the hydrological year (December–January) in order to calculate the net specific annual balance. Glacier 15 has lost an average of 600 mm of water a year since 1995 (11 years). The inter-annual variation is wide: very negative balances were observed in 1995 and 2002, two positive balances in 1999 and 2000, and negative balances for the remaining years. The dynamics of the glacier show a mass balance with very noticeable fluctuations. These variations are well synchronized with the glacier evolution. The variability of the ENSO (El Niño Southern Oscillation) has been an important factor in controlling the mass evolution of the Ecuadorian glaciers and the climate conditions. Those factors caused advances and retreats on the glaciers according to La Niña (cold event) or El Niño (warm event), respectively. This study has shown the relationship between glaciology and availability of hydrological sources.